Briggs & Stratton flywheel key. The flywheel key aligns the flywheel in the correct position on the crankshaft. If the engine stops suddenly due to hitting a hard object, the flywheel key shears in half to prevent damage to the engine. If the flywheel key is broken, the engine won't start.
50 pack of Flywheel Key 222698S. This key aligns the flywheel with the crankshaft for most Briggs & Stratton engines.